Forum Schedule Spring 2024

The ability to study matter under extreme pressures and temperatures has opened up a vast new playground for solid-state chemists to explore. No longer are elemental systems partitioned into those that form compounds and those that do not. Instead, the question has become: under what conditions do these systems form stable phases, and can these new phases be recovered? For materials scientists, extreme pressure represents a treasure trove of exotic compounds awaiting discovery—new materials that could propel next-generation or even as-yet unimagined technologies. In this talk, I will describe some new methods being developed in our lab that will empower solid-state chemists with the tools they need to target and recover new high-pressure phases. In particular, I will share some of our recent results on the discovery of novel transition metal carbides, demonstrating how our methods have allowed us to carry out the highly selective synthesis of high-pressure phases. I will also present results using nanosecond timescale X-ray diffraction to study materials in the shock-compressed state. These cutting-edge experiments allow us to study crystal structures under highly non-equilibrium conditions and might one day open up a completely novel approach to synthesis.

James Walsh is an Assistant Professor at the University of Massachusetts Amherst, where he began his independent career in 2019. James received his PhD in 2014 from the University of Manchester in the United Kingdom, working with Professor David Collison on the study of molecular nanomagnets. Following his PhD, James carried out research as a postdoctoral fellow at Northwestern working with Danna Freedman, where he studied high pressure as a tool for the synthesis of novel bismuth binary phases. His group’s research is supported by an NSF CAREER award (2022) and the ACS Petroleum Research Fund (2023).

Our group specializes in ultrafast spectroscopic methods, enabling in-depth studies of material chemistry in intricate environments and the control of quantum phenomena on femtosecond timescales. In the first part of this seminar, I will explore the pivotal role of lithium in diverse contexts - from its impact on symmetry-breaking in LiNbO3, to its unique properties in the quantum realm as seen in the polar metal LiOsO3, and to understanding the factors behind the reduced mobility of lithium ions on the surface of solid-state electrolytes like LixLa(2-x)/3TiO3. A commonality among these systems is the presence of lithium in a state where symmetry is broken, a phenomenon our group has adeptly investigated using extreme-ultraviolet second-harmonic generation spectroscopy (XUV-SHG). In the second part of the seminar, I will delve into our recent findings on 1T-TiSe2, a model compound known for its charge-density-wave (CDW) behavior and excitonic interactions at low temperatures. Our research utilizes cryogenic attosecond transient extreme-ultraviolet absorption spectroscopy (cryo-ATAS) and mega-electron-volt ultrafast electron diffraction (MeV-UED) to dissect the interplay of these complex phenomena. I will demonstrate how photoexcitation induces a dimensional shift in the CDW order parameter from 3D to 2D, a process governed by the system's excitonic correlations. This excitonic influence is further corroborated by the initial response in specific core-level absorption edges. These findings are instrumental in pinpointing the role of excitonic interactions in the CDW transition. Additionally, I will highlight the hidden one-dimensional nature of the CDW and its implications for the genesis of domain-wall-like topological defects, which are observed to form in less than a picosecond after photoexcitation.

Prof. Zuerch received his PhD in 2014 from the Friedrich Schiller University in Jena, Germany. Following a post-doc at UC Berkeley (2015-2017) with Leone and Neumark, he started an independent Max Planck Research Group at the Fritz Haber Institute in Berlin. In 2019 he joined the Department of Chemistry at UC Berkeley as Assistant Professor and is also a faculty scientist at the Lawrence Berkeley National Laboratory. He and his team experimentally explore structural, carrier and spin dynamics in novel quantum materials, heterostructures and on surfaces and at interfaces to answer current questions in materials science and physical chemistry. In this pursuit his group develops novel methods such as extreme-ultraviolet second-harmonic generation spectroscopy and unique instruments such as a cryogenic attosecond transient absorption spectrometer. Since 2020 he is the director of the California Interfacial Science Institute which is an effort funded by the University of California to advance the understanding of chemical processes at interfaces through experiment and theory. His work on linear and nonlinear XUV spectroscopy has been awarded the Fresnel Prize 2021 of the European Physical Society. He was also named a Hellman Fellow and won an W. M. Keck Foundation Science and Engineering Research Award. In 2023 he was awarded the DOE Early Career award.

While the exoplanetary field is replete with remarkable discoveries, perhaps the two most intriguing findings have been the detection of hot Jupiters – giant planets orbiting perilously close to their parent stars, and the startling abundance of super-Earths – a type of world entirely missing from our solar system. The mere existence of these worlds was wholly unpredicted based on the expectations that were gleaned from centuries of observation of our own solar system. This talk will delve into the demographics and orbital architectures of these exoplanets. We will explore how the sheer variety of observed exoplanetary systems can be reconciled into a unified theoretical framework.

Liquid sheets are freestanding laminar liquid structures which are produced using microfluidic nozzles. These liquid jets are optically flat and can have thicknesses ranging from tens of micrometers to just tens of nanometers. They are also vacuum stable, which makes them uniquely well suited for certain classes of X-ray experiments such as those performed at the Linac Coherent Light Source (LCLS) at SLAC. I will present recent developments with microfluidic devices which allow for the generation of flat, large-area liquid-liquid interfaces buried within the liquid sheets. These layered liquid sheets were then used as a platform for deep UV second harmonic generation (SHG) for tracking the temperature-dependent adsorption of ions to both the water-air and water-hydrocarbon interfaces. The two kinds of interfaces showed opposite thermodynamic trends indicating entirely different mechanisms of adsorption. Finally, I will present initial work on soft X-ray SHG on the water-vacuum interface from LCLS. This measurement is sensitive to the water surface structure through oxygen core electron transitions. The results were greatly complicated by competing X-ray photophysics but careful statistical analysis revealed a nonlinear response that was spectrally distinct from the bulk water absorption.

David J. Hoffman is an associate staff scientist at LCLS at the SLAC National Laboratory working with the ChemRIXS instrument. Prior to this he was a Research Associate at SLAC under a Laboratory Directed Research and Development program on developing multifluid liquid sheets for spectroscopic applications with Jake Koralek. He completed his graduate research at Stanford University in 2021 with Michael Fayer where he used 2D IR spectroscopy to examine chemical dynamics in liquids, glasses, and polymers.

Announcing the dawn of a new era of multi-messenger astrophysics, the gravitational wave event GW170817 – involving the collision of two neutron stars – was detected in 2017. In addition to the gravitational wave signal, it was accompanied by electromagnetic counterparts providing new windows into the different physics probed by the system. Since then, several gravitational wave events involving neutron stars have been discovered, with more expected over the next years.

In order to understand and interpret the physics of these events, it is necessary to model the intricate dynamics of such systems before, during and after merger, including the amplification of strong magnetic fields and the formation of hot and dense nuclear matter. Linking these multi-scale multi-physics dynamics to all observable channels (gravitational and electromagnetic) poses one of the main challenges of modern computational relativistic astrophysics and numerical relativity.

In this talk, I will discuss the state-of-the art numerical modeling of neutron star coalescence, including recent advances on the inclusion of advanced relativistic plasma and nuclear astrophysics in simulations.

Short gamma-ray bursts (GRBs) are now confidently associated with neutron star mergers. In the past decade, little attention has been paid to the extended emission, which lasts for about 100 seconds and is spectrally soft compared to the short-duration, hard prompt emission in these sources. We study the late-time accretion onto the merger remnant on previously unexplored timescales of minutes to hours and propose a simple model for the extended emission based on our findings. We further predict the existence of "orphan extended emission" (without the short GRB) as a promising EM counterpart for neutron star mergers, observable by current/future wide-field X-ray instruments like Einstein Probe and SVOM. This model also predicts narrow-band spectral features in the kilonova, potentially detectable by JWST.